Many carbonated beverages are packaged in bottles with removable screw caps threaded over the opening of the bottle. Pressurized gas in the headspace above the liquid in the bottle can develop a pressure of over 100 p.s.i. If the bottle closure is disengaged from the threads of the bottle before the underlying gas is sufficiently vented, the bottle closure can escape at rates of over 100 miles per hour: this problem is termed closure-missiling.
The problems of closure-missiling are most apparent with roll-on closures where a closure shell is forcibly threaded onto the neck of the bottle using the threads of the bottle to form matching threads in the closure shell. Frequently, a fixed annular element such as a depression or a ridge is provided on the bottle below the threads; the lower portion of the closure shell is rolled about the fixed element to secure the shell to the bottle. The portion of the shell engaging the fixed element is termed the tuck. The tuck is part of a pilfer-proof device which is partially perforated with vertical and/or horizontal slots spaced about the tuck. The tuck can be part of a solid ring attached by nibs to the upper portion of the shell so that the ring detaches at the nibs when the shell is initially rotated and remains behind after removal of the shell. Alternatively, the ring is partially perforated and splits upon rotation of the shell as it is lifted past the fixed element of the bottle and is removed with the shell. One such device is the Alcoa Eight-Score Pilfer-Proof Device.
Upon initial rotation of a conventional bottle closure, the pilfer-proof device is breached. As the closure continues to rotate, gas escapes between the closure and the threads of the bottle. Several patents have sought to enhance the venting after the breach of the pilfer-proof device. For example, Walker, U.S. Pat. No. 4,007,851, provides safety vents in the side walls of the closure proximate the top. Snyder, U.S. Pat. No. 4,007,848, discloses an anti-missiling bottle structure with channels passing through the threads of the bottle. The problem with these venting mechanisms is that closures which are misapplied to the bottle threads, that is, have not developed sufficient thread depth to engage the closure to the bottle threads, are retained primarily by the pilfer-proof device, which, once breached, completely disengages the closure from the bottle almost instantaneously. However, conventional devices such as those of Walker or Snyder contemplate a rotation of at least ten or twenty degrees, and preferably ninety degrees, to allow sufficient time for venting to occur. Bottle caps with misformed threads can missile before this amount of rotation is achieved.
Further, when similar forces strip or deform the threads and rupture the pilfer-proof device, the threads in the cap are freed from the bottle at the same time that the pilfer-proof device no longer secures the cap. No time is available for venting and missiling of the cap results.